patch 9.1.1226: "shellcmdline" completion doesn't work with input()

patch 9.1.1226: "shellcmdline" completion doesn't work with input()

Problem:  "shellcmdline" completion doesn't work with input().
Solution: Use set_context_for_wildcard_arg().  Fix indent in nextwild()
          (zeertzjq).

There are some other inconsistencies for input() completion (ref #948),
but since "shellcmdline" currently doesn't work at all, it makse sense
to at least make it work.

fixes: #16932
closes: #16934

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>